Photos of Campagnolo's Cambio Corsa
derailleur, courtesy of reader Richard Bryne. The special toothed
dropouts allowed the rear wheel to remain aligned in the frame while it
moved forward and backward to take up slack in the chain. For more
on the Cambio Corsa, click
here.

Two
levers--one released the rear wheel, the other shifted the
chain.

Special
dropouts meshed with teeth on the rear axle.

Note
the long dropouts. As on a fixed gear bicycle, the wheel moved
to take up slack in the chain.